Thermostat



Patented Sept. 29, 1936 ,ossszz UNITED STATES PATENT OFFlCE 2,055,922mmuos'rs'r William .1. ms. 'Soottdale, n. Application August 5, 1933,Serial No. 683,840

7 Claims. (CL 236'l02) This invention relates to thermostats, and moreparticularly to thermostats of the type used for regulating thetemperature of gas-fired ovens and the like, althoughnot necessarily solimited.

A difilculty common to thermostats of the character contemplated by theinvention as con= structed and used in the past is that due to thevarying temperature conditions maintainin in the walls of an oven inwhich they are used to and in supporting structure combined with thethermal elements proper, they are incapable of providing a preselectedtemperature in an oven until a relatively long period of time haselapsed after the oven is set in operation. Such period it frequentlyranges from thirty minutes to an hour and is often longer than the timerequired to treat many articles placed in the oven. Hence, either thearticles are not treated at the temperature intended, or elseconsiderable heat is wasted while go the user is waiting for thethermostat to become stable. As a rule such thermostats usually permitthe oven at starting to rise to a temperature considerably over thetemperature desired and then causes it to fluctuate for a considerabletime until the desired temperature is ly reached. For obvious reasons itis highly desirable to be able to provide for controlling an oven or thelike compartment in such way that it can be started and heated with amium of delay to so a. desired temperature, and such temperatureaccurately and dependably maintained when reached. With this in mind itis an object oi this invention generally stated to provide an improvedthermostat for uses of the nature referred 35 to above which is capableof controlling the oper-- ation of a gas-fired oven or the like in sucha way that the oven may be rapidly and gradually heated to a preselectedtemperature and such temperature. accurately and dependably maintainedas 40 soon as it is established.

A more particular object, however, is to provide in a thermostat forcompensating for the disturbing influence which the walls of an oven orthe like in which the thermostat is used and the 45 supporting structureof the associated parts of the thermostat have upon the thermal elementsproper.

These and various other objects, as well as the various other novelfeatures and advantages oi the invention, will be apparent when thefollowing detailed description is read in conjunction with theaccompanying drawings, of which Fig. l is a sectional view of an oventhermostat constructed in accordance with the invention; P18. 2

an elevational view of .the regulator end of such thermostat; and Fig. 3a view partly in section and partly in plan looking upwardly from thebottom of a modified form 0! the invention.

Reierring in detail to the drawing, and first more particularly to Figs.1 and 2, the numeral i 5 designates a valve casing of a type commonlyused in thermostats of this character, being made of relatively heavymaterial and divided into an in let chamber 2 and an outlet chamber 3 towhich suitable pipes 63 and it are connected lor con== ducting a i'ueisuch as a gas to a burner, not shown, which is employed to heat the ovenin which the thermostat is located. Seated in an opening 6 connectingthe inlet and outlet cham, hers oi? this casing there is provided asuitable valve l which is normally maintained on its seat by acompression spring 8 arranged between it and a removable cover 8 mountedon the outer end of the casing i. This covenas shown, is adapted to alsoengage the wall it of the oven and force it against a rib H on thecasing to hold the thermostat in place.

For operating the valve I, a highly expanslble tube is is threadablymounted in an opening to in the casing i and extended into the interioroi the oven, and within it there is arranged a valve-actuating rod I 4which is preferably made or some suitable material having an extremelylow or unappreciable coemcient of expansion.- As shown, this rod isextended through the valve l and the cover 9, although engaged in thevalve so as to open it when moved outwardly, andprovided at its outerend with a regulating wheel to for turning it to vary the operation ofthe valve as will presently appear. To prevent any leakage or fuel, asuitable packing I6 is provided about this rod is where it passesthrough the cover '9, and a calibrated dial IT is mounted opposite theregu- 'lating wheel which is provided with a pointer l8 stat.

to indicate the temperature setting 01 the thermo- In accordance withthe invention the thermal tube It is made as thin and light as ispermissible from the standpoint of strength so that it will follow asclosely as is possible the changes in temperaturein the oven, and alsoso that it will be influenced in its operation a minimum amount by theconduction of heatirom it to the valve casing during the period whensuch casing is being heated upto the temperature which the thermostatmay be set to maintain in the ove which, as is well known, will lag theheating of the thermal element and also that of the oven quiteconsiderably. As will be appreciated, by reason of its thinness suchtube will be able to take 55 on heat almost as rapidly as the casing canconduct heat from it, hence minimizing such conduction effect. I

To eliminate completely from the operation of the thermostat the eilfectupon it of the heatconducting action of the casing I and its associatedparts as well as the oven wall I I in which it is mounted, and also thatof the heat penetrating the thermostat parts, a compensating coupling orunion designated generally by the numeral I! is employed. This, asshown, con nects' the outer end of the thermal tube l3 to thevalve-actuating rod I4, and consists of a tube 2| which is closed at oneend and connected at the other to the tube I3 and an inner rod 22 whichis rigidly connected at one end to the valve-actuating rod I4 andadjustably connected at the other in the closed end of the tube 2|, thisadjustable connection being provided to allow for the regula- 20 tion ofthethermostat through the variation in to a stable temperature.

length of the rods I4 and 22 when the regulator wheel is turned.

To carry out its intended functions this latter coupling I9 is made upof an outer tube 2| formed of material, such as steel, having onecoeflicient of expansion and an inner tube 22 formed of material, suchas brass, having a different coefflcient of expansion. These. twomembers are so proportioned that the resultant movement which theyimport to the valve actuating rod I4 due to changes in their temperatureand their difference in coefllcient of expansion is in a directionopposite to that which the movement of the tube I3 tends to actuate therod l4 under the same condition of heating. In addition, these parts areso proportioned with respect to mass and dimensions that whenever theoven is heated there will be a delay in their reaching the temperatureof the oven which is equivalent to the delay occurring in thetemperature of the casing I reaching that of the oven. That is, they areso constructed as determined by the mass and construction of the casingI and the characteristics 01' the oven wall that they will justcompensate for the efiect on the thermal tube I3 which the casing I andthe other parts of the thermostat have upon thattube as a result of theheat which they exg ing, a control element mounted in said casing, a

tract from it while the oven is being brought up In other words, theyare so designed as to accurately compensate for the delay in expansionof the tube I 3 adjacent the valve casing I, which is caused by thedelay in such casing developing a stable temperature as the oven isheated. It will be understood, of course, that thisresult can beaccomplished through the use oi! other materials in the coupling unit I!by properly proportioning them andfd them as maybe determined byaccurate tests. Furthermore, for certain installations where'desired thecompensating unit may be constructed with a greater time lag than thesupporting casing has to provide a thermostat which will arrive rapidlyat a temperature somewhat below the temperature desired and then moregradually rise to the selected temperature and do so without'exceedingthe temperature which it is set to maintain.-

Another way. of practicing the invention is that shown in the embodimentillustrated in Fig.

it is larger and heavier than the thermal erement and hence a betterheat conductor it will require differently-proportioned elements than itdoes when mounted on the free end of the thermostat, as will be apparentto those skilled in the art.

According to the provisions of the patent statutes, I have explained theprinciple and mode of operation of my invention, and have illustratedand described what I now consider to represent its best embodiment.However, I desire to have it understood that, within the scope of theappended claims, the invention may be practiced otherwise than asspecifically illustrated and described.

I claim:

1. A thermostat comprising a supporting casing, a control elementmounted in said casing, a relatively light and highly expansible thermalelement for operating said control element, a motion-transmittingelement of negligible expansibility for operating said control elementin response to the movement of said thermal element, and athermal-connecting union having a reverse coefiicient of expansion tothat of the thermal element connected between said thermal element andthe motion-transmitting element and so proportioned as to accuratelycompensate for the efiect upon the thermal element of the heavier casingon which it is supported.

2. A thermostat comprising a supporting casing, a control elementmounted in said casing, a relatively light highly expansible thermaltube mounted in an opening in said casing, an operating 'rod ofrelatively low expansibility mounted in said-tube and connected to saidcontrol element, and means connecting said thermal tube to saidoperating rod comprising a tube made of one material connected to saidthermal tube and a rod made of another material connected between saidconnecting tube and said operating rod, said two connecting elementsbeing adapted to just compensate in the operation of said thermalelement for the eflfect upon it of the heat conducted from it by saidcasing when the thermostat is set in operation.

3. A thermostat comprising a supporting cashighly expansible thermalelement connected to said casing, an element of relatively low expan-'sibility connected to said thermal element and said control element forimparting to the latter the movement of the former, and means interposedbetween said thermal element and said motion-transmitting element whichis provided with a reverse coefilcient of expansion to said thermalelement and weight which delays its operation sufliciently to compensatefor the cflect produced upon the thermostat by the heat conducted fromthe thermal element to said casing until the latter reaches a stabletemperature.

4. A thermostat comprising a supporting casing, a control elementmounted in said casing, a thermally expansible element connected in anopening in said casing, a second thermally expansibleelement ofdifferent material connected to said first-mentioned thermal element, athird thermally expansible element made of a different kind or materialconnected to said second thermal element, and a non-expansible elementconnected between said third-mentioned element and said control element,said second and thirdmentioned thermal elements being provided with acombined coeflicient of expansion which just compensates for the effectupon the first thera non-expansible element connected to saidsecond-mentioned thermal element, and a third thermally expansibleelementv connected between said non-expansible element and said controlelement, said first and third-mentioned thermal elements being providedas a unit with a coeillcient of expansion which is contrary to that ofsaid second mentioned expansible element and is of a value determined bythe construction of said latter part whereby they are adapted toaccurately compensate in said thermostat for the eflect upon saidsecond-mentioned thermal ele-' ment of the heat-conducting action ofsaid casing as said casing is being heated to a stable temperature.

6. A thermostat comprising a supporting casing, a control elementcarried thereby,xand a heat-responsive assembly for thermallycontrolling with precision the operation of said control element, saidassembly consisting of a highly expansible element tor actuating saidcontrol element, an'element of low expansibility for transmitting themotion of said highly expansible element to said control element. and athermal coupling comprising one element connected in series with saidcontrol element and said low expansible element and another elementconnected in series with said highly expansible element and said casingand having a combined coeflicient of expansion which is negativelyexpansible as compared in effect on the control element to said highlyex-. pansible element and adapted by the construction or said couplingelement to compensate for the effect upon the entire assembly of theheat absorbed by said casing.

7. A thermostat comprising a supporting cas-, ing, a control elementmounted in said casing, a thermal unit disposed to eflect movement ofsaid control element and consisting'of a highly expansible member and amember of low expansibility which are connected to produce a resultantmovement in said control element and a second thermal unit arranged tomodify the movement which said first unit tends to impart to saidcontrol element, said latter thermal unit comprising two members ofdifferent coefllcients of expansion arranged to produce a movement insaid control element which is opposed to the direction of movementproduced thereon by the first-mentioned unit.

' -WILLIAM J'. BRENNEN.

